During operation of an internal combustion engine, fuel and lubricant deposits accumulate and bake onto the intake valves and intake ports of the fuel system. These deposits restrict the flow of air and fuel entering the combustion chamber which can cause stalling and hesitation, especially during "cold-start" operation.
Conventional detergents such as polyalkenyl succinimides as gasoline detergent additives are described as effective in providing carburetor cleanliness and port fuel injector cleanliness. However, the polyalkenyl succinimides alone offer little intake valve cleanliness performance. U.S. Pat. No. 5,089,028, incorporated herein by reference, discloses polyalkenyl succinimide-containing detergent fuel additives providing such performance which utilize carrier fluids having low temperature fluidity and solvency. Such fluids can include polymers or copolymers of olefinic hydrocarbons, aliphatic or aromatic carboxylic acid esters, polyethers, and synthetic or mineral oils such as solvent refined naphthenic mineral oils. However, such carrier fluids can be expensive and difficult to prepare. In any event, the substitution of lower cost substituents for such fluids would be advantageous.
Many hydrocarbonaceous mineral streams contain some small proportion of diamondoid compounds. These high boiling, saturated, three-dimensional polycyclic organics are illustrated by adamantane, diamantane, triamantane and various side chain substituted homologues, particularly the methyl derivatives. These compounds have high melting points and high vapor pressures for their molecular weights and have recently been found to cause problems during production and refining of hydrocarbonaceous minerals, particularly natural gas, by condensing out and solidifying, thereby clogging pipes and other pieces of equipment. For a survey of the chemistry of diamondoid compounds, see Fort, Jr., Raymond C., The Chemistry of Diamond Molecules, Marcel Dekker, 1976.
In recent times, new sources of hydrocarbon minerals have been brought into production which, for some unknown reason, have substantially larger concentrations of diamondoid compounds. Whereas in the past, the amount of diamondoid compounds has been too small to cause operational problems such as production cooler plugging, now these compounds represent both a larger problem and a larger opportunity. The presence of diamondoid compounds in natural gas has been found to cause plugging in the process equipment requiring costly maintenance downtime to remove. On the other hand, these very compounds which can deleteriously affect the profitability of natural gas production are themselves valuable products.
The problem of deposition and plugging by solid diamondoids in natural gas production equipment has been successfully addressed by a controlled solvent injection process. Alexander and Knight U.S. Pat. No. 4,952,748 teaches the process for extracting diamondoid compounds from a hydrocarbon gas stream by contacting the diamondoid-laden hydrocarbon gas with a suitable solvent to preferentially dissolve the diamondoid compounds into the solvent. Cullick and Roach U.S. Pat. No. 5,016,712 teaches a method for locating the solvent injection point within the natural gas wellbore.
Further studies have revealed that separation of the diamondoid compounds from the diamondoid-enriched solvent is complicated by the fact that numerous diamondoid compounds boil in a narrow range of temperatures surrounding the boiling range of the most preferred solvents. Alexander et al. U.S. Pat. Nos. 4,952,747, 4,952,749, and 4,982,049 teach various methods of concentrating diamondoid compounds in the solvent for, among other reasons, recycling the lean solvent fraction for reuse. Each of these processes produces an enriched solvent stream containing a mixture of diamondoid compounds. Chen and Wentzek U.S. Pat. No. 5,120,899 teaches a method for recovering diamondoids from a natural gas stream with a synthetic solvent which can be easily purified and recycled for continuous operation. The diamondoids recovered by the method of the '899 patent contain essentially no solvent contaminants.
Additional natural gas sources have now been discovered which produce a normally liquid mixture of diamondoid compounds, and, in accordance with the present invention, it has been found that these normally liquid diamondoid mixtures can be readily employed with detergent additives, e.g., polyalkenyl succinimides, e.g., as carrier fluids.